97 Tahoe whistling

[Mark97]

Sorry, couldn’t resist

Hahahaha!

If it whistled like that I might not mind it as much.

 

[Mark97]

Thanks for the other suggestions. That will give me a few things to check today. I'll let you know what I find later today.

 

[Mark97]

Ok. So this is what I found out today. The whistle only happens when the temperature control is set all the way cold. As soon as I get 4 "clicks" warmer, the whistle goes away. Does not fade out, it just stops.
Happens with the fan on or off. The a/c doesn't matter - on or off it whistles.
Until I go warmer, then it stops. I turn it back cold and the whistle starts again.

Tried every combination of idle, moving, a/c on or off, vent, feet, defrost. It blows hot and cold as appropriate. It just whistles when temperature is set to cold

The pic is the point where the whistling stops.

 

[OR VietVet]

Then that noise could be the controller itself, the connection at the back or the valve under the hood. When it is doing it is the noise inside or out?

The inside controller: https://www.rockauto.com/en/moreinfo.php?pk=85835&cc=1061367&jsn=930

The outside valve: https://www.rockauto.com/en/moreinfo.php?pk=84579&cc=1061367&jsn=982

Heater valve solenoid: https://www.rockauto.com/en/moreinfo.php?pk=1990462&cc=1061367&jsn=985

Or the plethora of connectors at the back of the controller.

 

[96-2D-Hoe]

Check the vacuum line to the heater control valve. There is a soloniod on the firewall and the hose from it should run to the heater control valve which is basically below the air filter. The heater control valve is a black plastic thing with two hoses in and two hoses out that run to the firewall. Link to image

https://www.rockauto.com/en/moreinfo.php?pk=84579&cc=1061356&jsn=753

 

[east302]

Sounds reasonable. The solenoid is energized when the temp dial is set to the “max” detent. That then applies engine vacuum to the heater valve.

The solenoid has a hard vacuum line running from the PCV fitting and across the intake. The soft vacuum line goes from the solenoid to the heater valve.

Sounds like the soft line could be disconnected/broken if it only happens when MAX is selected.

 

[Mark97]

Now that I know it's not an immediate mechanical issue, unfortunately this has gone down a couple slots on my to do list.
Hope to get to it in the next couple days - I will def let you know what I find.